This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2000-019452, filed Jan. 28, 2000, the entire contents of which are incorporated herein by reference.
The present invention relates to a torque control type impact wrench for producing torque by its hydraulic mechanism and controlling the produced torque and, more particularly, to a torque control type impact wrench for controlling torque by varying the rotation speed of a motor.
A prior art torque control type impact wrench includes an output shaft, a motor, an oil pulse unit for producing torque, and a torque sensor for sensing the torque. The motor rotates the oil pulse unit to develop oil pressure. The oil pulse unit converts the oil pressure into pulsed torque to rotate the output shaft and apply the torque to the output shaft.
A controller is electrically connected to the torque control type impact wrench to control the operation of the impact wrench. Before a fastening operation, the controller is supplied with criteria setting conditions suitable for male and female screws, i.e., the rotation speed of the motor and a cutoff torque value. The controller rotates the motor at the rotation speed and stops it when the produced torque exceeds the cutoff torque value.
The male and female screws are classified into three types of soft, rigid and intermediate parts according to a fastening characteristic or a relationship between a fastening torque and a fastening angle. The criteria setting conditions are determined with reference to the intermediate part. When an operator fastens the male and female screws of soft or rigid parts together, he or she controls and sets the conditions by experience and inputs them to the controller.
According to the prior art torque control type impact wrench described above, when the soft or rigid male and female screws, which differ from the intermediate screw in fastening characteristics, are fastened to each other, there are cases where the rotation speed of the motor is too low to produce an adequate torque because of inappropriate conditions input to the controller, and the screws are fastened insufficiently or excessively because of an improper cutoff torque value.
Furthermore, when an operator screws a plurality of male screws of the same specifications into their different fastening portions of female screws, he or she often fastens them under the same fastening conditions, though the fastening characteristics vary from fastening portion to fastening portion. Thus, the operator cannot fasten the screws appropriately.
It is accordingly an object of the present invention to provide a torque control type impact wrench that is capable of performing an appropriate fastening operation irrespective of the fastening characteristics and fastening portions of male and female screws.
In order to attain the above object, a torque control type impact wrench according to a first aspect of the present invention comprises torque producing means for producing pulsed torque, driving means for driving the torque producing means, a rotating shaft fitted to a predetermined male screw and rotated by the pulsed torque produced from the torque producing means, for screwing the male screw into a predetermined female screw, first setting means for setting an ideal upper limit of the pulsed torque for screwing the male screw into the female screw, second setting means for setting a driving speed at which the driving means drives the torque producing means, first storage means for storing the ideal upper limit of the pulsed torque, which is set by the first setting means, as a first storage value, second storage means for storing the driving speed, which is set by the second setting means, as a second storage value, and control means for causing the driving means to drive the torque producing means at the second storage value and stopping the driving means when the pulsed torque exceeds the first storage value, wherein the control means causes the second storage means to store a value, which is larger than the second storage value, as a new second storage value when the pulsed torque does not reach the first storage value within a given time period after the driving means starts.
The control means of the torque control type impact wrench so constituted allows the driving means to stop when the torque exceeds the ideal upper limit. The upper limit of the torque produced from the torque producing means can be considered to be an ideal upper limit of the torque for screwing the male screw into the female screw.
When the torque producing means cannot produce any fastening torque, which is not lower than the ideal upper limit, within a given time period after the driving means starts, the control means allows the second storage means to store a higher new speed in place of the driving speed stored in the second storage means, and causes the driving means to drive the torque producing means at such a higher driving speed that the torque producing means can produce torque that is not lower than the ideal upper limit. If the driving means drives the torque producing means at a higher driving speed, the torque producing means produces a higher torque, so that it can produce a fastening torque, which is not lower than the ideal upper limit, within a given time period after the driving starts. Typically, the control means increases the second storage value immediately after the driving means stops.
When the torque producing means cannot produce any fastening torque, which is not lower than the ideal upper limit, within a given time period after the driving means starts even though the driving means drives the torque producing means at the higher new speed, the control means can cause the second storage means to store a much higher new speed in place of the driving speed stored in the second storage means. This process can be repeated until the torque producing means produces a fastening torque, which is not lower than the ideal upper limit, within a given time period after the driving means starts. Typically, the driving means, the driving, and the driving speed correspond to rotating means, rotation, and rotation speed (number of rotations), respectively.
In the torque control type impact wrench according to the first aspect of the present invention, the impact wrench according to a second aspect of the present invention further comprises torque measuring means for measuring the torque, and the control means causes the second storage means to store a value, which is smaller than the second storage value, as a new second storage value when a maximum value of the torque measured by the torque measuring means exceeds the ideal upper limit by a given value or more.
The above torque measuring means so constituted measures the torque produced by the torque producing means and an excess amount of the torque that exceeds the ideal upper limit after the control means starts to stop the driving means. If the excess amount is larger than a predetermined tolerable value, the control means lowers the driving speed (second storage value) of the driving means and replaces it with a smaller new value to cause the excess amount to fall within a given range. Typically, the control means decreases the second storage value immediately after the driving means stops.
In the torque control type impact wrench according to the first aspect of the present invention, the impact wrench according to a third aspect of the present invention further comprises torque measuring means for measuring the torque, and the control means causes the first storage means to store a value, which is smaller than the first storage value, as a new first storage value when a maximum value of the torque measured by the torque measuring means exceeds the ideal upper limit by a given value or more.
The above torque measuring means so constituted measures the torque produced by the torque producing means and an excess amount of the torque that exceeds the ideal upper limit after the control means starts to stop the driving means. If the excess amount is larger than a predetermined tolerable value, the control means lowers a torque value (first storage value) for starting to stop the driving means, and replaces it with a smaller new value to cause the excess amount to fall within a given range. Typically, the control means decreases the first storage value immediately after the driving means stops.
When the above excess amount does not fall within a given tolerable range even though the driving means is stopped at the smaller new torque value, the control means can cause the first storage means to store a much smaller new value in place of the torque value stored in the first storage means. This process can be repeated until the excess amount falls within the given tolerable range.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.